The present invention relates to a rock drill and, more particularly, to a rock drill equipped with a tunnel profile control system.
In driving a tunnel, it is known to use an apparatus for automatically drilling blastholes. For example, Japanese Patent Publication No. 57-51518, first published Feb. 5, 1979, in the form of a laid-open version, discloses a rock drill mounted on a boom assembly, wherein during the drilling operation the position and the direction of each drilling point in an orthogonal coordinate system projected parallel to the tunnel face is converted into a value on a boom coordinate system for the boom assembly so that the position of the boom assembly can be controlled according to the value on the boom coordinate system before the actual drilling is performed in reference to a predetermined blasthole pattern.
The position and the direction of each blasthole are determined in consideration of the geological features of the ground to be excavated and other factors, and however, it often happens that after the actual blasting, the tunnel would be driven having its transverse sectional profile deviating from the designed profile. One of the major reasons for the deviation from the designed profile is the presence of rocks of varying hardness. Once the tunnel ceiling has been excessively excavated, a correspondingly increased amount of concrete is required for the tunnel lining, and on the other hand, extra excavation is required to form the designed tunnel ceiling.
Where the tunnel excavation is continued even though the transverse sectional profile of the tunnel being driven has deviated from the designed profile, without any corrective measures taken in such a way as to alter the blasthole pattern, it is obvious that the transverse sectional profile of the tunnel being driven is further deviated unless a favorable change in the nature of the rock being excavated is encountered. Successive deviation in transverse sectional profile of the tunnel being driven eventually results in the necessity of the increased amount of concrete for the tunnel lining; the longer the tunnel to be driven, the greater the amount. It also eventually results in the necessity of extra excavation work to be done.
In contrast to the prior art technique, it can be contemplated to minimize the deviation in tunnel sectional profile by surveying the tunnel sectional profile each time a cycle of excavating work completes, determining the geological difference of the material, through which the tunnel is being driven, in light of the magnitude of deviation measured from the designed sectional profile, and altering, on the basis of the determination, one or both of the designed blasthole pattern and the amount of explosives to be charged into the blastholes for the subsequent cycle of excavating work. However, where the tunnel to be driven has a large sectional profile, the profile survey cannot be accurately performed without difficulty, and, if possible with the use of a separate measuring apparatus specially designed only for the profile survey, the measuring apparatus must be of such a size and/or bulkiness that it will not disturb the freedom of movement of the automatic rock drill apparatus.